The results of this investigation demonstrate that the salutary effects of TNG on ischemic injury during acute myocardial infarction are mediated by an increase in collateral flow and a reduction in MVO2. However, if TNG causes hypotension (with resulting diminution in collateral flow) or exercise tachycardia (with resulting increase in MVO2 and perhaps decrease in flow), reduction of ischemic injury will not occur without addition of methoxamine to reverse the TNG-induced pressure and heart rate changes.